At the present time a very high percentage of all of the residential doors which are installed, for example, more than 70 percent and possibly as high as 90 percent, are supplied to builders as pre-hung door and jamb assemblies. Thus, the door is already mounted or hung in the jamb assembly at the factory by hinge means to one of the jamb members. The other side of the door will be formed with a lockset and knob opening and the jamb member will have a latch or striker plate opening.
Typically, pre-hung door and jamb assemblies are shipped to the installation site from the factory with the jamb member opposite the door hinges either fastened directly to the edge of the door or spaced from the door edge by a plurality of shipping stabilizers. Sometimes the shipping stabilizers are merely thin pieces of wood, paper or cardboard that is nailed or adhesively secured between the door and jamb and held in place by strapping.
In other instances, L-shaped stabilizing brackets have been provided which are bolted into the edge of the door and the front of the jamb. This stabilizing bracket and bolt system, for example, is more commonly used on commercial metal pre-hung doors by manufacturers such as Stanley Tools.
In most cases, when the door is received at the installation site, the jamb member opposite the hinges is freed or unfastened. The stabilizer members are usually left in place, if they are the cardboard variety, or removed, if they are metal L-shaped brackets. There would be no practical way to remove the metal bracket stabilizers if the doors were installed with them in place. While the door is hinged to one side of the jamb assembly, removal of the spacers and/or unbinding of the assembly frees the opposite door jamb member to move relative to the door. The door assembly installer must position the door in the door opening, do the necessary shimming between the door opening and the jamb members so as to mount the door assembly in a squared-up relationship inside the door opening. Moreover, the stabilizers are usually thinner than the desired reveal space between the door and jamb, so the installers manipulate the jamb to produce the desired reveal space, usually establishing the reveal space by eye. During this process, two installers are often employed, particularly to control the free or lockset side of the door. Using conventional installing techniques approximately 20 to 30 minutes will be required to install a pre-hung door. This is a significant time savings over doors which are not pre-hung, but it still represents a significant amount of time, particularly when two installers are employed.
French or double doors are even more difficult to install. While they are hinged at the opposed jamb members, the doors at the center will be free to move, once the assembly is unpacked and the shipping fasteners and stabilizers are removed. Moreover, since the bottoms of the jamb members are not connected, they are free to diverge, making plumbing of the door in the door opening a difficult and time-consuming job.
The difficulties in connection with manipulating pre-hung door assemblies can compromise the quality of the installation. Installers with less experience and patience will install pre-hung doors in varying degrees of skew, particularly when the door openings are roughly constructed, which is almost always the case.